1. Field of the Invention
The present invention relates to an image sensor unit used in an image reading apparatus, such as a copying machine, image scanner, facsimile and so on, and the image reading apparatus using the image sensor unit. In particular, it relates to an image sensor unit that reads image information from a recording medium, such as a bill, security and so on, and an image reading apparatus that authenticates the recording medium.
2. Description of the Related Art
For example, Japanese Laid-open Patent Publication No. 2007-116590 discloses an image reading apparatus that handles a bill.
With such an image reading apparatus, a gap of a predetermined dimension is formed between an image sensor unit and a light source unit for transmission reading to allow smooth passage of a bill. The illuminance distribution of illumination light emitted by a light source for reflection reading (in particular, the illuminance distribution in the direction of the normal to the bill passing through the apparatus) is preferably uniform. If the illuminance distribution is nonuniform, the illuminance of the light illuminating the bill differs between a part of the bill that passes through a point closer to the image sensor unit and a part of the bill that passes through a point closer to the light source unit for transmission reading if the bill moves in the direction of the normal thereto or is creased. Then, there is a possibility that the illuminance of the reflection light from the bill is nonuniform, and the reading accuracy deteriorates.